1. Technical Field
The present invention relates to a droplet ejection apparatus.
2. Background Art
In an ink jet recording apparatus, which is one type of droplet ejection apparatus, when the apparatus has been left without carrying out a printing operation for a long time, a degree of ink viscosity in a recording head may be increased due to vaporization of a solvent in the ink (for example, water in the case of water-soluble ink) through ejection ports (nozzles) of the recording head (hereinafter, it is also referred to as “thickening ink”), or a relatively large bubble may occur in the ink due to intrusion of air on an ink supply system or growth of a minute air bubble that has been in the ink originally. Once such increase of the degree of ink viscosity or occurrence of the air bubble arises in an ink channel, which is communicated with the ejection hole of the recording head, or the like, the ejection operation of the recording head is not carried out normally even though a printing operation is carried out after the apparatus is powered on again.
In order to deal with such ejection failure due to the causes, the ink jet recording apparatus may carry out recovery processing including, for example, a capping process in which an ejection hole surface of the recording head is covered with a cap to prevent the thickening of the ink, a pump-suction process in which the ink is sucked through the ejection hole by a pump or the like with a capping state to discharge the thickening ink, a flushing process in which ink is ejected onto a predetermined ink receiver including an ink absorber and the like to discharge the thickening ink, and the like.
When a conventional ink jet recording apparatus is powered on subsequently, the apparatus automatically carries out predetermined recovery processing that combines any of the recovery processes described above, or the user makes the recording apparatus carry out the recovery operations described above if needed.
However, in the apparatus that carries out the above-mentioned recovery operation automatically, for example, in the case where the apparatus is used in a manner to be powered on and off frequently and repeatedly, because a left time thereof becomes relatively short, it is often the case that the recovery operation is not carried out necessarily every power-on time. In this case, there is a problem that ink is consumed necessarily.
On the other hand, in the case where the recovery operation is carried out in accordance with decision of the user, ink may be ejected onto an ink receptor (for example, paper) according to a test pattern, and the user may check presence or absence of an ejection failure with his or her eyes. However, there is a problem that the ink and the ink receptor are wasted. Further, it is necessary for the user to have knowledge of the ejection failure, which lead to a problem that it is difficult to use the recording apparatus.
In view of these problems, a method of carrying out the recovery operation by changing recovery conditions of the recording head (such as the flushing operation, pump-suction operation) according to the time until the power of an ink jet recording apparatus is turned on again after the power thereof was turned off has been proposed as a method of reducing useless consumption of ink as much as possible and preventing an ejection failure from occurring (for example, Japanese Laid-Open Patent Application No. Hei. 6-1222306 or the like).
However, because it is easy for ink to thicken at low temperature and drying and to the contrary it is difficult for ink to thicken at high temperature and high humidity, the amount of discharged ink required to carry out the recovery processing in elapsed time varies greatly according to the conditions. Because the apparatus is not provided with means for detecting influence due to the conditions in the method disclosed in the above-mentioned Patent Application, the recovery processing has to be set in anticipation of safety. Thus, because there is the case that ink is discharged more than necessary, such an operation is wasteful.
Further, the user, in effect, has to judge with his or her eyes whether or not all the nozzles corresponding to the ink ejection operation are recovered to normal states by the recovery processing on the basis of the output result onto a sheet of paper or the like. Thus, it is not necessarily user friendly. Moreover, because clock means is necessary to carry out the conventional method, components of the apparatus are increased, and this causes the cost increases.